/* Copyright 2023 Dual Tachyon
 * https://github.com/DualTachyon
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *     Unless required by applicable law or agreed to in writing, software
 *     distributed under the License is distributed on an "AS IS" BASIS,
 *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *     See the License for the specific language governing permissions and
 *     limitations under the License.
 */

#include "ARMCM0.h"
#include "systick.h"
#include "../misc.h"

// 0x20000324
static uint32_t gTickMultiplier;

void SYSTICK_Init(void) {
    SysTick_Config(480000);
    gTickMultiplier = 48;
}

void SYSTICK_DelayUs(uint32_t Delay) {
    const uint32_t ticks = Delay * gTickMultiplier;
    uint32_t elapsed_ticks = 0;
    uint32_t Start = SysTick->LOAD;
    uint32_t Previous = SysTick->VAL;
    do {
        uint32_t Current;

        do {
            Current = SysTick->VAL;
        } while (Current == Previous);

        uint32_t Delta = ((Current < Previous) ? -Current : Start - Current);

        elapsed_ticks += Delta + Previous;

        Previous = Current;
    } while (elapsed_ticks < ticks);
}

void SYSTICK_Delay250ns(const uint32_t Delay) {
    const uint32_t ticks = (Delay * gTickMultiplier) >> 2;
    uint32_t i = 0;
    uint32_t Start = SysTick->LOAD;
    uint32_t Previous = SysTick->VAL;

    do {
        uint32_t Delta;
        uint32_t Current;

        do Current = SysTick->VAL;
        while (Current == Previous);

        Delta = (Current < Previous) ? -Current : Start - Current;
        i += Delta + Previous;
        Previous = Current;

    } while (i < ticks);
}
